A contact structure of a metal and a semiconductor in which a voltage-current characteristic has a rectifying property, that is, current easily flows at a voltage in an arbitrary direction but current hardly flows at a voltage in a reverse direction is referred to as a Schottky junction. A direction of the voltage at which the current easily flows is referred to as a forward direction and a direction of the voltage at which the current hardly flows is referred to as a reverse direction.
The Schottky junction has a rectifying property because a potential barrier is formed at the junction due to different functions of the metal and the semiconductor. For example, when a function of the metal is higher than that of the semiconductor at a junction of a metal and an n-type semiconductor, a potential barrier for electrons is formed at the junction to become a Schottky junction. When a positive voltage is applied from the metal to the semiconductor at this junction, the potential barrier is lowered and electrons in the n-type semiconductor flow to the metal so that current flows.
When the voltage is applied in a reverse direction, the potential barrier becomes higher, so that the flow of the electrons from the metal to the semiconductor is blocked and the current hardly flows. When the function of the metal is lower than that of the n-type semiconductor, the potential barrier for electrons is not formed so that the Schottky junction is not formed. Further, when the function of the metal is lower than that of a P-type semiconductor at the junction of the P-type semiconductor and the metal, the potential barrier for holes is formed to become a Schottky junction.
In order to control the Schottky junction according to the related art, an additional process is required to vary the type of metal or semiconductors.